In a long-sought step toward building a safer mosquito, researchers have infected the insects with persistent bacteria that sabotage their malaria-causing parasites.

Researchers would like to use Wolbachia bacteria to keep malaria parasites from thriving inside a mosquito. In theory, a mosquito with the right bacterial infection could bite people without delivering the parasites that cause malaria.

Wolbachia naturally infect insects from butterflies to cockroaches — but not some disease-spreadi...